1. Field of the Invention
The present invention relates to a water heater that heats water from a water supply pipe using a heat exchanger provided with a burner, and that delivers hot water from a hot water delivery pipe.
2. Description of Related Art
A water heater can deliver hot water at a predetermined temperature to a bathroom etc. from a hot water delivery pipe. A water supply pipe, to which water is supplied from a public water supply, is connected to the inlet side of a heat exchanger that is provided with a burner. A hot water delivery pipe is connected to the outlet side of the heat exchanger. When water flows into the heat exchanger in the water heater via the water supply pipe, the water is heated by heat exchange between the burner combustion gas and the water.
However, it is well known that in areas with a high level of water hardness, after years of use, scale builds up in the heat exchanger. Due to this build-up of scale, the heat transfer efficiency of the heat exchanger deteriorates, and a fin temperature rises, thus leading to deterioration in heat efficiency. Furthermore, if use is continued in this state, the precipitation and build up of scale increases, and eventually a heat exchanger tube cracks and leaks water. As a result, the water heater can no longer be used. Here, as disclosed in Japanese Patent Application Publication No. JP-A-2003-254615, an invention is known in which an abnormal temperature sensor is provided in the heat exchanger. When the abnormal temperature sensor detects a temperature equal to or greater than a pre-set specified temperature as a result of a heat rise after shut off of the hot water supply, it is determined that abnormal heating of the heat exchanger has occurred as a result of deteriorated heat efficiency due to the build-up of scale. In the conventional device, the abnormal heating is notified to a user and a maximum burning capacity value of the burner is lowered, when delivery of hot water is restarted. Therefore, the water heater where the scale is built up can be used even before it is repaired.
However, the above-mentioned invention disclosed in Japanese Patent Application Publication No. JP-A-2003-254615, simply allows temporary use of the water heater during and after the build-up of scale, and the water heater does not remove the scale itself. In the end, special maintenance is necessary to remove the scale.